Interelectrode separator for rechargeable batteries



April 14, 1953 M. N. YARDNEY ETAL INTERELECTRODE SEPARATOR FOR RECHARGEABLE BATTERIES Filed May 5, 1951 A sinfered DI nus IN V EN TORS H m @6 AA W M f T KM M MM T N. E G. A

Patented Apr. 14, 1953 INTERELECTRODE SEPARATOR FOR RECHARGEABLE BATTERIES Michel N. Yardney, New York, and Martin E.

Kagan, Bronx, N; Y., assignors to- Yardney International Corp., New York, N. Y., a corporation of New York Application May 5, 1951, Serial No. 224,708

,11 Claims. 1

The present invention relates to electric batteries, more particularly to. batteries of the rechargeable silver-and-zinc type.

In various co-pending applications assignedto the assignee of the present application, such as Ser. No. 738,702, filed April 1, 1947, 66,291 and 66,292, filed December 20, 1948, 197,730, filed November 27, 1950, all issued April 29, 1952 as Patents Nos. 2,594,709, 2,594,710, 2,594,711 and 2,594,713, respectively, and Ser. No. 131,320, filed December 6, 1949, now Patent No. 2,601,133, issued June 17, 1952, there have been disclosed rechargeable batteries wherein one or more positive electrodes, consisting essentially of silver, and one or more negative electrodes, consisting essentially of zinc and/or zinc compounds, are immersed in an alka line electrolyte and are spaced from oneanother by semi-permeable separators or membranes, the entire assembly being held in compression in a suitable casing;

The separators employedinthebatteries heretofore described consisted either of regenerated cellulose (cellophane) or a combination of one or morecellophane layers with an additional layer or layers of a more permeable material, such as porous, absorbent paper; in-the latter case it had been found advantageous to insert the more permeable layer or layers between the cellophane and the active electrode material in order to 1 protect the cellophane from direct contact with the electrode materialwhich could give riseto undesirable chemical reactions. It is a property of these separators to swell in the alkaline electrolyte and, by virtue of having been introduced with a relatively tight fit into the battery casing along with electrodes of substantially non-compressible, compact material, toexert pressure upon the electrodes and to be themselves compressed to prevent undue dilation of their interstices. 1

In the development of batteries adapted to be recharged a large number of times the need has arisen for providing a non-conductive separator whose semi-permeable characteristics (including the ability toswell and to exert pressure) should be similar to those of cellophane yet which should exhibit even greater ability to withstand repeated chargings and dischargings without a method of lastingyly protecting'adjacent electrodes fromcontact with one another while enabling the passage of ions between them.

In accordance with the present invention there is provided, as a separator between electrodes of a battery as set forth above, at least one layer of polyvinyl alcohol, either alone or in combination with a layer or layers of cellophane and/orof a more porous material such as natural cellulosic paper (i. e. paper left in its naturally absorbent state, such as filter paper, Aldex paper, blotting paper). The polyvinyl alcohol may be a simple polymer with unlinked chains, or its chains may be cross-linked with the aid oi suitable agents such as bifunctional aldehydes, alcohols or acids. In the latter case greater mechanical and chemical stability is obtained, at the expense of a slight decrease in the permeability of the membrane which may be compensated, in terms of internal cell resistance, by reducing the number and/or the thickness of the layers used. Furthermore, a more crystalline and, hence, mechanically and chemically more resistant molecule structure may also be'obtained by placing the membraneunder tensile stress, as by wrapping it in stretched condition around an electrode.

.Amongthe agents adapted to form the crosslinkagesbetween the polyvinyl alcohol chains of the membrane there may be mentioned oxalic acid, :malonic acid, itaconic acid, formaldehyde, and glyoxal.

, The accompanying drawing shows, schematically and by way of example, a battery con structed in accordance with therpresent invention.

iThe battery shownin the drawing comprises a housing 19 wherein there are assembled twonegative electrodes Ha, llb and a positive electrode 12v sandwiched between the former. The active material of the negative electrodes is comminuted zinc which inthedischarged condition of the battery is oxidized to ZnO (and possibly also hydrolized, at least in part, to' Zll(OI-I)a); the active material of the positive electrode is comminuted silver which may be sintered as described in co-pending application Ser. No. 174,076, filed July 15, 1950. Negative leads 13a, I319, merging at 13, and a positive lead l4 project from the negative electrodes Ha, Ho and from the positive electrode l2, respectively.

The electrodes Ila and Nb are individually wrapped in sections I511, 15b of a generally U- shaped envelope 15 of porous paper, as described in co-pending application Ser. No. 153,830; an envelope l6 of cellophane surrounds the positive electrode l2. Between the positive electrode assembly l2, It, on the one hand, and the negative assembly Ila, Ilb, l5a, 15b, on the other hand, there is interposed a semi-permeable separator in the form of a membrane l1, this membrane consisting of polyvinyl alcohol which may or may not be cross-linked as described above. An electrolyte (not shown) of potassium hydroxide, saturated with zinc, permeates the entire assembly which is held under pressure in the casing ID.

The membrane I1 is preferably stretched when winding it about the electrode 12, the resulting tension being maintained, for example, by heatsealing the overlapping edges of the membrane as indicated at 18.

Although the polyvinyl alcohol separator ll has been shown in the drawing as an envelope completely surrounding the electrode I 2, it should be understood that the same may also be used, instead, as a simple sheet placed between two electrodes, as a wrapper around a negative electrode, and so forth, and that in general this separator may be given any of the configurations disclosed for the cellophane separators in the various co-pending applications mentioned above. Also, the layers of porous paper and of cellophane shown in the drawing may be omitted or interchanged, or additional such layers may be included. Furthermore, it should be noted that at least part of the zinc of the negative electrode may be replaced by a different electronegative material, e. g. cadmium, and that at least part of the silver of the positive electrode may be similarly replaced by a different electropositive material, e. g. nickel.

What is claimed is:

1. A battery comprising a casing, an alkaline electrolyte in said casing, a positive and a negative electrode of substantially non-compressible, compact material in said electrolyte, and a membrane of polyvinyl alcohol interposed between said electrodes and permeated by said electrolyte, said electrodes and said membrane forming part of an assembly fitting tightly inside said casing, said permeated membrane exerting pressure upon said electrodes in said casing.

2. A battery according to claim 1 wherein each of said electrodes comprises a comminuted active material.

3. A battery according to claim 2 wherein the :active material of said positive electrode contains silver and the active material of said negative electrode contains zinc.

4. A battery according to claim 1 wherein the active material of said negative electrode contains zinc and said electrolyte is saturated with Z1110.

5. A battery according to claim 1, including means maintaining said membrane under ten sion.

6. The combination according to claim 1 wherein the polyvinyl alcohol is modified by means of an agent forming cross-links between the chains of said alcohol.

7. The combination according to claim 6 wherein said agent is selected from the group which consists of bifunctional alcohols, aldehydes and acids.

8. A battery according to claim 1 wherein said negative electrode contains an active material selected from the group which consists of zinc and cadmium.

9. A battery according to claim 1 wherein said positive electrode contains an active material selected from the group which consists of silver and nickel.

10. A battery comprising a casing, an alkaline electrolyte in said casing, a positive and a negative electrode of substantially non-compressible, compact material in said electrolyte, a membrane of polyvinyl alcohol interposed between said electrodes and permeated by said electrolyte, and at least one layer of a porous, non-conductive material inserted between said membrane and at least one of said electrodes, said electrodes, said membrane and said layer forming part of an assembly fitting tightly inside said casing, said permeated membrane exerting pressure upon said electrodes in said casing.

11. A battery comprising. a casing, an alkaline electrolyte in said casing, a positive and a negative electrode of substantially non-compressible, compact material in said electrolyte, a membrane of polyvinyl alcohol interposed between said electrodes and permeated by said electrolyte, and at least one layer of cellophane inserted between said membrane and at least one of said electrodes, said electrodes, said membrane and said layer forming part of an assembly fitting tightly inside said casing, said permeated membrane exerting pressure upon said electrodes in said casing.

MICHEL N. YARDNEY. MARTIN E. KAGAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Re. 22,065 Young Apr. 7, 1942 2,176,427 Kershaw Oct. 17, 1939 2,256,105 McConnell Sept. 16, 1941 2,420,456 White May 13, 1947 2,422,045 Ruben June 10, 1947 2,448,052 Roberts Aug. 31, 1948 2,519,399 Roberts Aug. 22, 1959 2,566,114 Bloch Aug. 28, 1951 2,594,709 Andre Apr. 29, 1952 2,594,710 Andre Apr. 29, 1952 2,594,711 Andre Apr. 29, 1952 2,594,712 Andre Apr. 29, 1952 2,594,713 Andre Apr. 29, 1952 OTHER REFERENCES Vinyl Products Bulletin, V. 7-1148 on EL- VANOL by DuPont.

Nye (Abstract), S. N. 627,080, January 17, 1950. 

1. A BATTERY COMPRISING A CASING, AN ALKALINE ELECTROLYTE IN SAID CASING, A POSITVE AND A NEGATIVE ELECTRODE OF SUBSTANTIALLY NON-COMPRESSIBLE, COMPACT MATERIAL IN SAID ELECTROLYTE, AND A MEMBRANE OF POLYVINYL ALCOHOL INTERPOSED BETWEEN SAID ELECTRODES AND PERMEATED BY SAID ELECTROLYTE, SAID ELECTRODES AND SAID MEMBRANE FORMING PART OF AN ASSEMBLY FITTING TIGHTLY INSIDE SAID CASING, SAID PERMEATED MEMBRANE EXERTING PRESSURE UPON SAID ELECTRODES IN SAID CASING 